1. Field of the Invention
The present invention relates generally to power converters, and relates more particularly to a dual buck-boost power converter with independent regulation.
2. Description of Related Art
Dual buck-boost converter topologies are available for a number of applications. Typically, two different power supplies create two separate outputs. The two separate outputs are often a positive voltage output and a negative voltage output.
Referring to FIG. 1, a buck-boost converter with two inputs and two outputs is illustrated as circuit 10. Circuit 10 includes two of each component, such as two switches S1, S2, two diodes D1, D2, two inductors L1, L2 and two capacitors C1, C2. The two power supplies, indicated as circuit 12 and 13, each have a separate feedback circuit to provide a closed loop control. Circuit 12 and 13 each use a reference voltage in conjunction with a feedback voltage value to determine modulation of the voltage to duty cycle conversion. In circuit 10, two separate inputs of +/−5V are used to generate the two separate outputs, +Vout and −Vout. In addition, there are typically two separate loads, negative load 14 and positive load 15.
In circuit 10, switches S1 and S2 are operated to control power output to loads 14 and 15 according to the desired set point determined by voltage Vref. In controlling the output to loads 14 and 15, inductors L1 and L2 are separately charged or discharged. Accordingly, circuit 10 uses two separate inductors that typically are realized as external components due to their size. That is, the majority of components in circuit 10 can be formed in an integrated circuit with the noted exception of inductors L1 and L2. The use of two inductors also adds cost to the circuit in terms of component cost and increased size that is realized in constructing the converter.
An alternative to circuit 10 provides a buck-boost converter that drives a positive and negative output voltage on alternating cycles of the controller respectively. This alternate method uses one inductor, but suffers from being less efficient in power density and device utilization. The outputs of this alternative prior circuit using a single inductor also has very high ripple voltage on both outputs +Vout and −Vout.
In some buck-boost solutions that deliver dual outputs, a load balancer is sometimes used to help maintain the output voltages at consistent and opposite levels. However, the load balancer typically draws extra power by shunting voltage or current, and reduces the overall efficiency of the power converter.
Accordingly, it would be desirable to obtain a buck-boost converter with a dual output and single inductor with improved efficiency and performance.